History
A 6-year-old spayed female Miniature Schnauzer was evaluated because of lethargy, signs of abdominal pain, anorexia, and intermittent vomiting of 1 week's duration. Abnormal physical examination findings included fever (39.8°C [103.6°F]) as well as approximately 8% dehydration and signs of abdominal pain. Serum biochemical analysis and a CBC revealed moderate neutrophilic leukocytosis with a left shift and toxic changes, mild thrombocytopenia, mild hypernatremia, and hypochloremia. Urinalysis revealed severe proteinuria, isosthenuria (urine specific gravity, 1.017), severe leukocyturia, and bacteriuria (numerous rod bacteria). Radiographs of the abdomen were obtained (Figure 1).
Left lateral (A) and ventrodorsal (B) radiographic views of the abdomen of a 6-year-old spayed female Miniature Schnauzer examined because of lethargy, signs of abdominal pain, anorexia, vomiting, dehydration, and fever.
Citation: Journal of the American Veterinary Medical Association 246, 12; 10.2460/javma.246.12.1289
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
On the lateral radiographic view, the borders of only one kidney are visible (Figure 2). The other kidney may be superimposed on the visible kidney or other abdominal organs. The visible kidney is normal in size but has an irregular border, which is ill-defined cranially and caudally. The surrounding retroperitoneal space has decreased contrast caused by a heterogeneous mixture of fat and soft tissues opacities. These changes are suspected to have a perirenal distribution. The descending colon is displaced ventrally, which could be in part secondary to a mass effect from the retroperitoneal space. The liver appears reduced in size, and congenital vertebral malformations are seen at the thoracolumbar and lumbosacral junctions. On the ventrodorsal view, the left kidney is faintly visible and appears normal in size and shape. A mild increase in soft tissue opacity is evident in the region of the right kidney. Radiographic differential diagnoses include retroperitoneal effusion, steatitis, or infiltration. Possible causes are neoplasia (involving the kidney or the adrenal gland), inflammatory pathological process, and urinary tract rupture or hemorrhage.
Same radiographic images as in Figure 1. A—Notice the irregular kidney (arrows) and the mixed soft tissue opacities in the retroperitoneal area (asterisks). B—There was a mild increase in soft tissue opacity in the region of the right kidney (arrows).
Citation: Journal of the American Veterinary Medical Association 246, 12; 10.2460/javma.246.12.1289
Abdominal ultrasonography was performed to better characterize the retroperitoneal space and to evaluate the kidneys and adrenal glands. An irregularly shaped, enlarged right kidney with a hyperechoic cortex and moderate pyelectasia was evident (Figure 3). On the right side, the retroperitoneal space contained a considerable amount of fluid with heterogenic echogenicity, surrounded by highly hyperechoic retroperitoneal fat. Ultrasonographically, the left kidney, adrenal glands, and other abdominal structures were normal in appearance.
Sagittal ultrasonographic image of the right kidney of the dog in Figure 1. Notice the moderate pyelectasis (arrow), adjacent retroperitoneal fluid accumulation (asterisks), and hyperechoic surrounding fat (hash marks). The image was obtained transabdominally with a 5- to 8-MHz curvilinear transducer.
Citation: Journal of the American Veterinary Medical Association 246, 12; 10.2460/javma.246.12.1289
Treatment and Outcome
The retroperitoneal fluid was aspirated with a 22-gauge needle under ultrasound guidance. A thick hemorrhagic purulent exudate was retrieved. Cytologic evaluation revealed a large amount of degenerate neutrophils, erythrocytes, and large numbers of intra- and extracellular rod bacteria. The retroperitoneal effusion also had high concentrations of creatinine (effusion concentration, 188 μmol/L [serum concentration, 103 μmol/L]) and potassium (effusion concentration, 41 mmol/L [serum concentration, 3.8 mmol/L]). These findings were compatible with a uroseptic retroperitoneal effusion. Bacterial culture later revealed a heavy growth of Escherichia coli.
The dog underwent emergency laparotomy within a few hours after initial evaluation. Preoperatively, the dog received IV fluid therapy and antimicrobials (enrofloxacin and ampicillin). A right nephrectomy was performed after the kidney was found to be diffusely leaking a large volume of purulent material into the retroperitoneal space. The kidney was highly vascularized with tortuous blood vessels arising from the retroperitoneum. No other abnormalities were found. The abdomen was profusely lavaged and closed over an active suction drain.
The patient underwent cardiorespiratory arrest at the end of the procedure and could not be revived. The dog had become severely hypotensive during anesthesia and was unresponsive to aggressive fluid therapy and vasopressor agents.
Histologic evaluation of the right kidney revealed severe pyonephritis (ie, purulent inflammation of the kidney) resulting in severe suppurative necrotizing retroperitoneal inflammation. Severe renal tubular degeneration and necrosis were also present.
Comments
The dog of the present report was a middle-aged patient with pyonephritis, secondary uroseptic retroperitoneal effusion, and severe suppurative retroperitoneal necrotizing inflammation. In one previous case report,1 a retroperitoneal abscess was suspected to be caused by pyelonephritis, but the abscess did not contain urine. Other reports22–4 described the presence of pyonephrosis, resulting in outflow obstruction and hydronephrosis, but without retroperitoneal contamination.
Further diagnostic imaging, such as excretory urography or positive contrast pyelography, could have been considered to identify a leak from the kidney or ureter into the retroperitoneal space. The presence of hyperechoic retroperitoneal fat increased the index of suspicion for an inflammatory process within the retroperitoneal space. That suspicion coupled with the gross appearance of the retroperitoneal effusion lead to immediate in-clinic fluid analysis and cytologic evaluation and diagnosis of retroperitoneal bacterial infection and urine leakage. On the basis of these findings, an emergency exploratory laparotomy was elected to remove the source of infection and lavage the retroperitoneal space and abdomen.
References
1. Hylands R. Veterinary diagnostic imaging. Retroperitoneal abscess and regional cellulitis secondary to a pyelonephritis within the left kidney. Can Vet J 2006; 47: 1033–1035.
2. Szatmári V, Osi Z, Manczur F. Ultrasound-guided percutaneous drainage for treatment of pyonephrosis in two dogs. J Am Vet Med Assoc 2001; 218: 1796–1799.
3. Schaer M. Pyonephrosis in the cat and dog. Clinical view. Clinician's Brief 2010;Sep:66–67.
4. Choi J, Jang J, Choi H, et al. Ultrasonographic features of pyonephrosis in dogs. Vet Radiol Ultrasound 2010; 51: 548–553.
